Comparative molecular field analysis of the binding of the stereoisomers of fenoterol and fenoterol derivatives to the β₂ adrenergic receptor

Stereoisomers of fenoterol and six fenoterol derivatives have been synthesized and their binding affinities for the β₂ adrenergic receptor (K_iβ₂-AR), the subtype selectivity relative to the β₁-AR (K_iβ₁-AR/K _iβ₂-AR) and their functional activities were determined. Of the 26 compounds synthesized in the study, submicromolar binding affinities were observed for (R,R)-fenoterol, the (R,R)-isomer of the p-methoxy, and (R,R)- and (R,S)-isomers of 1-naphthyl derivatives and all of these compounds were active at submicromolar concentrations in cardiomyocyte contractility tests. The K_iβ₁-AR/K _iβ₂-AR ratios were >40 for (R,R)-fenoterol and the (R,R)-p-methoxy and (R,S)-1-naphthyl derivatives and 14 for the (R,R)-1-napthyl derivative. The binding data was analyzed using comparative molecular field analysis (CoMFA), and the resulting model indicated that the fenoterol derivatives interacted with two separate binding sites and one steric restricted site on the pseudo-receptor and that the chirality of the second stereogenic center affected K_iβ₂ and subtype selectivity.